WET ASSAYS. 121 



When pure, sulphide of antimony contains a little more 

 than 70 per cent, of metal 



WET ASSAYS. 

 Gold. 



Powder about half an ounce of ore. Add four times its 

 weight in a mixture of 4 parts hydrochloric and 1 part 

 nitric acid, in an evaporating dish or other apparatus. 

 Evaporate the decanted solution to dryness, hydrochloric 

 acid being added as evaporation proceeds. Add sulphate 

 of iron, dissolved in water, to the gold solution, both being 

 previously warmed. The gold is precipitated as a brown 

 powder. Filter the solution and weigh the dry precipitate. 



This method, however, is not to be recommended so 

 much as the dry assay. 



Silver. 



Dissolve the powdered ore in nitric acid, and throw down 

 the chloride of silver precipitate by adding a solution of 

 common salt or else hydrochloric acid.* If chloride of lead 

 and mercurous chloride are absent, the solution may be 

 decanted or filtered, and the chloride of silver weighed : 

 three-quarters of the weight very nearly represents pure 

 silver. Or else the chloride of silver may be fused and the 

 metallic silver collected and weighed. 



Lead. 



Place the powdered ore in a porcelain dish or other con- 

 venient and suitable apparatus, and thoroughly dissolve it 

 in strong nitric acid by heat until the residue is nearly white 

 and red fumes cease to be given off. Add a few drops 

 of sulphuric acid and evaporate to dryness ; then add water, 

 and filter. As silica and certain sulphates may be in the 

 residue, boil it along with carbonate of soda for about forty 

 minutes. Filter. Dissolve the residue carbonate of lead, 

 &c. in acetic acid. Add a little sulphuric acid to the 



* Ammonia added to the precipitate would dissolve the chloride of 

 silver, would blacken the mercurous chloride, and would not alter the 

 chloride cf lead. 



